The body includes various passageways such as arteries, other blood vessels, and other body lumens. These passageways sometimes become occluded or weakened. For example, the passageways can be occluded by a tumor, restricted by plaque, or weakened by an aneurysm. When this occurs, the passageway can be reopened or reinforced, or even replaced, with a medical endoprosthesis. An endoprosthesis is typically a tubular member that is placed in a lumen in the body. Examples of endoprostheses include stents and covered stents, sometimes called “stent-grafts”.
An endoprosthesis can be delivered inside the body by a catheter that supports the endoprosthesis in a compacted or reduced-size form as the endoprosthesis is transported to a desired site. Upon reaching the site, the endoprosthesis is expanded, for example, so that it can contact the walls of the lumen.
When the endoprosthesis is advanced through the body, its progress can be monitored, e.g., tracked, so that the endoprosthesis can be delivered properly to a target site. After the endoprosthesis is delivered to the target site, the endoprosthesis can be monitored to determine whether it has been placed properly and/or is functioning properly.
Monitoring of the position of the endoprosthesis during implantation is typically performed by a radiographic technique such as fluoroscopy. The radiographic density of the metal endoprosthesis is different from bone and tissue, and the device is observed in the fluoroscopic image from the visible difference in contrast and grey scale relative to the surrounding biological material. The disadvantage of fluoroscopy is that the physician, staff, and patient are exposed to ionizing radiation which can be harmful in strong or repeated doses.
Another method of monitoring a medical device is magnetic resonance imaging (MRI). MRI uses a magnetic field and radio waves to image the body. In some MRI procedures, the patient is exposed to a magnetic field, which interacts with certain atoms, e.g., hydrogen atoms, in the patient's body. Incident radio waves are then directed at the patient. The incident radio waves interact with atoms in the patient's body, and produce characteristic return radio waves. The return radio waves are detected by a scanner and processed by a computer to generate an image of the body.